from collections import deque
class Solution(object):
    def updateMatrix(self, matrix):
        """
        :type matrix: List[List[int]]
        :rtype: List[List[int]]
        """
        if not matrix or not matrix[0]:
            return matrix
        m, n = len(matrix), len(matrix[0])
        res = matrix[:]
        
        q = deque()
               
        for i in range(m):
            for j in range(n):
                if matrix[i][j] == 0:
                    q.append([[i, j], 0])

        dx = [1, -1, 0, 0]        
        dy = [0, 0, 1, -1]
        visited = [[0 for _ in range(n + 1)] for _ in range(m + 1)]

        while q:
            tmp, distance = q.popleft()
            x0, y0 = tmp[0], tmp[1]

            if matrix[x0][y0] == 1:
                res[x0][y0] = distance

            for k in range(4):
                x = x0 + dx[k]
                y = y0 + dy[k]

                if 0 <= x < m and 0 <= y < n and visited[x][y] != 1:
                    q.append([[x, y], distance + 1])
                    visited[x][y] = 1
        return res
                    
                    
                    
    
            